Method for extracting anions

ABSTRACT

The invention relates to a method of extracting anions based on metals of groups IV B to VIII of the periodic table from aqueous solutions thereof, wherein compounds of general formula                    
     are used as extractants, in which a maximum of two of the R 1 , R 2 , R 3  and R 4  substituents represent hydrogen atoms and the remaining substituents represent identical or different alkyl or aminoakyl groups, which are optionally branched and which contain on average at least 5 C atoms.

This application is the National Stage Application of PCT/EP99/09914,which claims a priority from German Applications 198 59 683.9 filed Dec.23, 1998.

BACKGROUND

The present invention relates to a method of extracting metals of groupsV to Vll of the periodic table, which exist in the form of anions,metal-containing anions or anionic metal complexes, from aqueoussolutions. Extraction from aqueous solutions by means of an organicphase which is insoluble in the aqueous phase and which contains anextractant is a purification step which is widely used during theproduction of pure metals of groups V to VIII of the periodic table.Extraction methods are firstly used for the separation of impuritieswhich arise from the respective raw materials and which are present indigestion solutions. and secondly are also used for the separation ofelements which are adjacent in the periodic table and which cannot beobtained, or which can only be obtained with difficulty, by othermethods of separation on account of their chemical affinity. Inparticular, the separation of pairs of elements comprising W/Mo. Ta/N.Co/Ni and V/Cr is very important industrially. Moreover, extraction isalso used as a vehicle for the chemical reaction of sodium tungstate toform ammonium paratungstate, for example. This is achieved by contactingan aqueous solution of sodium tungstate with an organic phase, whereuponthe tungstate ions are transferred to the organic phase. and afterseparating the organic and aqueous phases tungsten cations are strippedfrom the organic phase with aqueous ammonia solution.

In extractive separation. use is made of the pH- and/ortemperature-dependent selective loading capacity and/or of the differentloading kinetics of the organic phase with respect to different ions.

Extraction is usually conducted in multi-stage mixer-settler cascades orcolumns, using counter-current flow.

In addition to the requirement of selectivity of the extractant or ofthe organic phase with respect to the ions to be separated. theextractant or the organic phase has to have as high a loading capacityas possible at room temperature and must have an approximately neutralpH. Moreover, the extractant should exhibit a solubility in water whichis as low as possible, and for process technology reasons the organicphase should not have too high a viscosity.

Known solvent extraction methods only fulfil the aforementionedrequirements inadequately, so that there is a desire for improvedextraction methods, and particularly for improved extractants. Thus theextraction of cobalt in particular is effected by means of tertiaryamines and quarternary ammonium salts, which result in a loading of 10to 15 g/l cobalt. Higher loadings of 10 to 25 g/l cobalt can be achievedby the use of organophosphoric acids (DEHPA phosphonic acids, phosphinicacids), but there is a risk here of contaminating the cobalt withphosphorus. Moreover, the selectivity in relation to nickel is low. Theextraction of molybdenum is mainly carried out by the use of secondaryamines as extractants at loadings of 38 to 42 g/l in the organic phase.In the extraction of tungsten with secondary amines, loadings of 60 to70 g/l W are achieved, whereas tertiary and quarternary amines merelyresult in a loading of 12 to 15 g/l W.

DE-A 2 530 244 discloses a method of extracting heavy metals by theformation of complexes with amino alkanols. However, amino alkanols ofthis type have the disadvantage that their solubility in water is toohigh for industrial use. According to EP-A 505277, iron and zirconiumare separated from lanthanide/actinide mixtures by means ofpropanediamides. The publication by DU PREEZ in Mineral Processing andExtractive Metallurgy Review, 15 (1995) pg. 153 to 161, discloses theuse of tetra-substituted diamines for chloro complexes of mono- anddivalent metals.

It has now been found that alkyl-substituted 1,3-diaminopropanes areoutstandingly suitable for the extraction of anions based on metals ofgroups V to VIII of the periodic table from aqueous solutions thereof.Moreover, a surprisingly high loading capacity has been found comparedwith the primary, secondary or tertiary amines and quarternary ammoniumcompounds which have been customary hitherto.

DESCRIPTION

Accordingly, the present invention relates to a method of extractinganions based on metals of groups IV B to VIII of the periodic table fromaqueous solutions thereof which is characterised in that compounds ofgeneral formula

are used as extractants, wherein a maximum of two of the R¹, R², R³ andR⁴ substituents represent hydrogen atoms and the remaining substituentsrepresent identical or different alkyl or aminoalkyl groups. which areoptionally branched and which contain on average at least 5 C atoms.

The anions based on metals of the groups IV B to VIII of the periodictable can be the corresponding metal-containing anions (metalates) oranionic metal complexes.

The sum of the C atoms of the R substituents divided by the number ofsubstituents which are not hydrogen atoms should amount to at least 5,so that sufficient insolubility in water is ensured. The average numberof C atoms of the R substituents which are not hydrogen atoms shouldpreferably be not more than 10, in order to keep the viscosity of theextractant low, which is advantageous as regards process technology. Thepreferred extractants according to the invention which correspond to theabove formula are characterised in that R² and R⁴ are hydrogen atoms.The preferred substituents R¹ and R³ are nonyl groups which areoptionally branched, most preferably isononyl groups which areoptionally branched.

The extractant is preferably used together with an organic solvent whichis not soluble in water. Suitable solvents include high-boiling mixturesof hydrocarbons, which may comprise aliphatic. cycloaliphatic andaromatic organic compounds. High-boiling solvent napthas, such as thosewhich can be obtained, for example, from the TOTAL company under thetrade name Spirdane® HT, are particularly preferred.

The extractant according to the invention is also preferably used incombination with isodecanol (IDA) as a modifier.

The organic phases which are preferably used according to the inventionare those which contain 0.5 to 95% by volume of diaminopropanederivatives, up to 99% by volume of diluent and 0.5 to 20% isodecanol.The organic phases which are most preferably used contain 10 to 20% of adiaminopropane derivative, 5 to 15% isodecanol and 65 to 85% of anorganic solvent.

The extraction method according to the invention can be carried out overa temperature range from 15 to 80° C. Temperatures within the range from20 to 60° C. are preferred.

The aqueous phase can have a pH of 1 to 10, depending on the ions to beextracted.

The method according to the invention is particularly suitable for theextraction of tungsten from solutions which contain molybdenum andtungsten. Solutions of tungsten in caustic soda which result fromdigestion with caustic soda after the separation of impurities(particularly P, As, Si, Al, Ti, V, Nb, Ta, Sn) by precipitation or ionexchange at pH 8 to 9 can be used directly for extraction. Theextractive separation of tungsten and molybdenum is advantageouslyconducted at a pH of the aqueous phase of 7 to 8.5, most preferably at apH of 7.3 to 8.2. By comparison: the extraction of tungsten withsecondary amines necessitates a pH lower than 6, and a pH of 2 to 3 isrequired in order to achieve high loadings; extraction with quarternaryammonium compounds necessitates a pH of 7 to 7.5, but tungsten can onlybe partially stripped with ammonia so that molybdenum/tungstenseparation can only be achieved by adding a sulphite. According to theinvention, a loading of the organic phase corresponding to about 120 g/ltungsten and less than 2 mg/l Mo is achieved at a pH of about 8. Anotheradvantage of the comparatively high pH of the method according to theinvention is that carbon dioxide can advantageously be used as a mineralacid in order to adjust and maintain the pH. In order to recoverammonium paratungstate (APT), the loaded organic phase is stripped withammonia solution in the manner known in the art after separation of theaqueous phase.

Another method which is preferred according to the invention is theextractive separation of cobalt and nickel from aqueous solutions whichcontain cobalt and nickel ions. The cobalt and nickel ions arepreferably present as chlorides in the aqueous solution. Extraction ofcobalt from the aqueous solution necessitates a low pH, i.e. it isconducted in the presence of free hydrochloric acid at a preferredconcentration of 150 to 250 g/l of free HCI, so that the cobalt ispresent as a chloro complex.

The examples below are illustrative example in which all parts andpercentages are by weight unless otherwise indicated.

EXAMPLES

The aqueous feed solution and the organic phase (OP) were introducedinto a separating funnel, intensively mixed, and separated by allowingthe phases to stand.

In the (simulated) two-stage extraction, the OP was twice brought intocontact with fresh feed solution. The extraction tests were performed atroom temperature (25° C.).

Example 1

OP: 20% N,N-bis-(isononyl)-1,3-diaminopropane 10% isodecanol 70%Spirdane HT feed solution: 90 g/l Co as chloride 10 g/l Ni as chloride200 g/l free HCl quantitative ratio OP: feed = 1:1 OP loading after2-stage 30.8 g/l Co extraction: 0.15 g/l Ni.

OP loading after 2-stage extraction:

30.8 g/l Co

0.15g/l Ni.

Example 2

OP: as in Example 1 feed solution: 91.7 g/l Mo as Na₂MoO₄ quantitativeratio OP: feed = 1:1 pH: 7.3, adjusted with H₂SO₄ OP loading after2-stage extraction: 43 g/l Mo.

Example 3

OP: as in Example 1 feed solution: 111 g/l W as Na₂WO₄ 60 mg/l Moquantitative ratio OP: feed = 1:1 pH: 7.5, adjusted with H₂SO₄ OPloading after 2-stage extraction: 122 g/l W <2 mg/l Mo.

Example 4

OP: as in Example 1 feed solution: 937 g/l V as Na₂VO₃ quantitativeratio feed: OP = 2:1 pH: 6.3, adjusted with H₂SO₄ OP loading after1-stage extraction: 60 g/l V.

Example 5

OP: as in Example 1 feed solution: 35 g/l Cr as Na₂Cr₂O₇ quantitativeratio feed: OP = 1:1 pH: 1.8, adjusted with H₂SO₄ OP loading after1-stage extraction: 33 g/l Cr.

Example 6

OP: as in Example 1 feed solution (acidified with HF): 103 g/l Ta 62 g/lNb 25 g/l Ti quantitative ratio feed: OP 1:1 OP loading after 1-stageextraction: 66.6 g/l Ta 33.1 g/l Nb 3.8 g/l Ti.

Example 7

OP: 10% N,N-bis-(isononyl)-1,3-diaminopropane 10% IDA 80% Spirdane HTfeed: 60 g/l W as Na₂WO₄ 90 mg/l Mo quantitative ratio feed: OP = 1:1 pHadjusted with H₂SO₄ (variable) OP loading after 1-stage see FIG. 1.extraction:

FIG. 1 show s the percentages of the metals which were transferred tothe OP as a function of pH.

Although the present invention has been described in detail withreference to certain preferred versions thereof, other variations arepossible. Therefore, the spirit and scope of the appended claims shouldnot be limited to the description of the versions contained therein.

What is claimed is:
 1. A method comprising extracting anions based onmetals of groups IV B to VIII of the periodic table from aqueoussolutions thereof with an extractant of general formula:

wherein a maximum of two of the R¹, R², R³ and R⁴ substituents representhydrogen atoms and the remaining substituents represent identical ordifferent alkyl or aminoalkyl groups, which are optionally branched andwherein the sum of the C atoms of the R substituents divided by thenumber of substituents which are not hydrogen atoms is at least 5 Catoms.
 2. The method according to claim 1, wherein R² and R⁴are hydrogenatoms.
 3. The method according to claim 1, wherein R¹ and R³ are nonylgroups which are optionally branched.
 4. The method according to claim1, wherein the extractant is used in combination with a diluent.
 5. Themethod according to claim 1, wherein the extractant is used incombination with isodecanol as a modifier.
 6. The method according toclaim 1, wherein the aqueous solution contains tungsten and molybdenumanions and tungsten anions are extracted at a pH of 7.5 to 8.5.
 7. Themethod according to claim 1, wherein the aqueous solution containsanions which contain cobalt and nickel and cobalt anions are extracted.